The drying of skins and hides constitutes a fundamental change in the water balance of the proteins which participate in the building-up of the skin. In particular, the protein materials which are located between the collagen fibers and which are water soluble in the natural state, but which are less responsible for the skin structure, are denatured, whereby the collagenous bundles of fibers, responsible for the elasticity and strength of the skin, stick together (agglutinate) and harden. The absorption of water is thereby greatly obstructed after dehydration of the skins.
It is known to soften hides and skins enzymatically in the neutral and slightly alkaline pH ranges by means of enzymatic agents, with and without an additive of wetting agents. The non-structured protein materials which cause the skin fiber network to agglutinate and obstruct the softening process, are decomposed and dissolved out. In this manner, the softening and returning of the hides and skins to the natural swollen state by absorption of water are considerably accelerated.
Processes for the enzymatic softening of furs which are performed by using proteolytic enzymes, have already been described in German Patent Specifications Nos. 847,947, 941,680, 972,832, and 976,602.
However, all the proteases used in these processes have the disadvantage that either the pickling or softening effect is inadequate, or a certain amount of loosening of the hair has to be accepted. Thus, the above-mentioned patent specifications recommend working at acid pH values, or the joint use of carbohydrases, although this does not achieve the object in a really satisfactory manner. For this reason, German Offenlegungsschrift No. 16,69,353 describes a process for loosening the fibrous structure of furs in which the enzyme takes effect only after the tanning agent takes effect.
In accordance with German Patent Specification No. 18,00,891, the same enzymes are used for softening as are used for depilation, the enzyme concentrations being, of course, reduced by the factor 10 in the former field of application and the pH value being adjusted to 3 to 4. It is obvious that, under these conditions, either the risk of loss of the hair has to be accepted or an optimum softening effect has to be foregone.